I have a 91 GTA 5.7 and have the following problem. When starting from cold about 1 min after starting the engine note noticably changes starts to run very rough and the service light comes on. Once the engine has warmed up, if I turn off wait a few minutes then re-start the engine runs slightly better and the light does'nt come on. I have retrieved the error code and get 42. Could anyone give me a clue where to start looking.I live in the U.K and am having difficulty finding a reliable garage close to where I live. Thanks in advance.

 

Code 42 referrs to the Electronic Spark Timing (EST) module. Check to make sure that the bypass wire connector is making good contact - it is the connector that is disconnected to set the base timing - near the blower motor. If each of the 4 wires has continuity (less than 4 ohms, on the lowest ohms scale) from the ECM to the EST module in the distributor, then replace the EST module.

Any pack rats been in the engine compartment? If so, they may have chewed through the wires to the EST module.

While you are in the distributor, check for continuity (on the highest ohms scale) from one of the pick up coil wire terminals (that plugs into the EST module) to ground - it should be an open circuit - if not, replace the pick up coil, too.

Tim

 

Many thanks for your help. This gives me somewhere to start.